"That does mean then that they have been paid for something they didn't have to deliver, and is therefore an extra cost."

Oh, come on - first you're complaining that the money is NOT being spent, now you're complaining that it IS being spent. How about if the school busses just drive around and burn up gas during the strike, and the school cooks make lunches and then throw them out? That would keep everything going along nicely, wouldn't it?